This invention relates to a nut assembly used to fasten an instrument or the like to a member to the back of which hands cannot reach.
FIGS. 4A-6 show a conventional nut assembly used for such purpose. As shown in FIGS. 4A and 4B, the nut assembly 1 comprises a nut 5 having a threaded through hole 2 and pins 3 on both sides and formed at one end thereof with an inclined guide surface 4 for pivoting the nut when pushed by a bolt A, and a frame 9 having a pair of opposed arms 8 provided on both sides of a flange portion 7 having a bolt hole 6 at the center. By supporting the pins 3 in elongated holes 10 formed in the arms 8, the nut 5 is mounted between the opposed arms 8 so as to pivot about the pins 13) 3 and to be slidable in and along the elongated holes 10.
Lugs 11 are provided on both sides of the nut 5 so that with the pins 3 positioned at the tips of the elongated holes 10, the nut 5 can turn only 90 degrees in one direction from the position in which the longitudinal direction of the nut 5 is aligned with the longitudinal direction of the arms 8 and can slide along the elongated holes 10 from the position in which the longitudinal direction of the nut 5 is perpendicular to the longitudinal direction of the arms 8. Further, at the tips of the arms 8, lugs 12 are provided which are adapted to engage the lugs 11 when the longitudinal direction of the nut 5 is aligned with the longitudinal direction of the arms 8.
The flange portion 7 of the frame 9 is rectangularly shaped. Around the bolt hole 6 in the flange portion 7, a bolt guide wall 13 for axially guiding a bolt A inserted through the bolt hole 6 is provided so that the bolt will be reliably threaded into the threaded hole 2.
The nut 5 has on its back side a ridge 14 having an apex extending in the longitudinal direction, and has a threaded hole which extends therethrough in substantially the center thereof. The side of the threaded hole 2 into which the bolt A penetrates is formed into a tapered guide hole 15 so that the bolt A can easily penetrate into the threaded hole 2. The open end of the guide hole 15 has such an inner diameter that the bolt guide wall 13 fits therein.
Thus, the inner diameter of the threaded hole 2 is uniform from the guide hole 15 to its end where it opens at the ridge 14 on the back side.
FIG. 6 shows the conventional nut assembly 1 inserted into a hole D formed in the member B. It shows how an instrument C is fastened to the member B by means of a bolt A tightened into the nut assembly 1. As shown in FIG. 6, the nut assembly 1 is inserted into the hole D with the nut 5 first and further pushed in until the flange portion 7 abuts the surface of the member B. With an instrument C superposed on the flange portion 7 of the nut assembly 1, the bolt A is inserted into a hole E of the instrument C while pushing the inclined guide surface 4 of the nut 5 with the tip of the bolt, thereby turning the nut 5 by 90xc2x0. The tip of the bolt is guided into a tapered guide surface 15 of the nut 5 so as to threadedly engage female threads of the threaded hole 2. When the bolt is turned further, the nut 5 is pulled close. The mounting is now complete.
As shown in FIGS. 5A and 5B, in this conventional nut assembly 1, since the nut 5 has a horse-saddle shaped ridge 14 on its back side, the last thread of the threaded hole 2 at the ridge 14 is defined as a partially missing incomplete circle. Thus, if female threads 2a are formed by tapping on the inner periphery of the hole 2, incomplete female threads will be formed at the end.
In particular, some of the female threads 2a near the end tend to be shaped into independent small ribs as shown in FIG. 5B.
In the manufacturing steps of such nuts 5, after formation of the female threads 2a, the nuts are generally subjected to polishing or plating. In these steps, the nuts 5 collide against each other, so that the ridge 14 on the back of each nut collides against the edge portions of other nuts 5. When the edges of other nuts collide against the end of the threaded hole 2, small ribs of the female threads 2a formed in the previous step are liable to be deformed.
This is because the ridge 14 has a shape similar to a horse saddle and the threaded hole 2, formed in it, is completely unprotected against deformation.
If small threads are deformed, when the bolt A is threaded and its tip is about to protrude to the back side, the male threads of the bolt A and the deformed portions of the female threads 2a will engage, so that the bolt A will be unable to advance.
Since ordinary nuts can be rigidly held by hand or tool, deformation of such a degree poses no practical problems in many cases. But with the nut to which this invention is directed, if meshing occurs with the nut simply supported by the arms 8 extending from the flange 7 of the frame 9 in a hollow portion to which hands cannot reach, even such a slight meshing causes the nut 5 to be turned together with the bolt A. The arms 8 may thus be broken.
Thus, it was required to form female threads of a size slightly larger to allow slight deformation of the threads at the end of the threaded hole, or a high degree of quality control was required.
An object of this invention is therefore to provide a nut assembly in which the open end of the threaded hole formed in the nut at the ridge formed on the back side is a complete circle so that since due to protection against external shocks, deformation will not occur at the end of the female threads during polishing or plating, no special consideration is needed in the formation of female threads.
According to this invention, there is provided a nut assembly comprising a pivotable nut having a threaded through hole and a pin on each side thereof, and a frame having a flange portion formed with a bolt hole and an opposed pair of arms extending from both sides of the flange portion, the arms each being formed with an elongated hole, the nut being formed at one end thereof with an inclined guide surface for pivoting the nut when pushed by a bolt, the nut being pivotably and slidably mounted between the arms with the pins received in the elongated holes formed in the arms, characterized in that the nut is of an elongated cubic shape, is formed with a threaded hole which extends therethrough substantially in the center thereof from one of its longitudinal sides toward its back side, and is integrally formed on the back side with a ridge, and that a hole is provided coaxially with the threaded hole where one end of the threaded hole opens at the ridge, the hole having an inner diameter substantially equal to or greater than the root diameter of the female threads formed in the threaded hole.
In this invention, since the hole provided in the ridge has an inner diameter substantially equal to or greater than the root diameter of the female threads of the threaded hole, female threads are scarcely formed in the hole provided in the ridge. At the boundary between the hole, which is an incomplete circle, and the end of the threaded hole, which is a complete circle, a tapered surface can be formed.
The bolt penetrating side of the threaded hole is formed into a tapered guide surface so that the bolt can easily advance into the threaded hole.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: